Data packet access schemes that employ selective retransmissions to communicate data packets are widely used in wired and wireless communication systems to provide more efficient use of resources and high data rate services. Commonly used technologies in, for example, a Third Generation Partnership Project (3GPP) compliant system include Adaptive Modulation and Coding (AMC), Hybrid Automatic Repeat Request (HARQ), and serving grant allocation.
To enable HARQ, a data receiver sends control signals back to a data transmitter to acknowledge if the data was received successfully or not. Such signals may be a single bit and are commonly referred to as acknowledgment/negative acknowledgment (ACK/NACK) signals. If the data transmitter receives a NACK, the same packet of data, with possible change of data rate matching and bit rearrangement, is sent again. Otherwise, a new packet of data is sent. The success or failure of data reception is primarily driven by the propagation channel condition and overall signal-to-noise plus interference ratio. To enable AMC, the data receiver sends a channel quality indicator (CQI) to the data transmitter, by which the data transmitter can adaptively select a proper data packet size and modulation type to achieve higher throughput.
Additionally, to enable serving grant allocation, such as that used in high speed uplink packet access (HSUPA), a NodeB informs a user equipment (UE) of the maximum allowed transmit power to maintain high quality of the service in terms of data throughput, as well as to reduce the interference among users.
In wireless communication, many techniques have been developed to mitigate the impact from propagation channel conditions. One technique developed for frequency domain duplex (FDD) wireless communications is closed-loop transmit diversity. In this technique, a data packet in an FDD wireless communication signal is transmitted from a first unit over multiple antennas with a selected complex weight applied to each of the antennas. The complex weights are generated at the data receiver of a second unit based on signals received from the first unit to meet certain criteria, such as to maximize the received signal-to-noise ratio. The weights generated by the second unit are sent back to the first unit to be applied to the first unit's data transmission, forming the closed-loop.
FIG. 1 illustrates an example functional block diagram where a first wireless transmit receive unit (WTRU) 10 has a data transmitter 12 that transmits data packets over two transmit antennas 14a, 14b where selected weights are applied to the transmissions from the antennas 14a, 14b via respective mixers, 15a, 15b. The first WTRU 10 also includes a receiver 16 which is configured to receive feedback response, such as ACK/NACK signals and CQIs as well as antenna weights generated by a second WTRU 20 that receives the transmitted signals from the first WTRU 10. The receiver 16 distributes the ACK/NACK signals and CQIs to the transmitter 12 via path 17 and the received antenna weights to the mixers 15a, 15b, via path 18. Accordingly, in addition to having a packet data receiver 22, the second WTRU 20 has a feedback generator 24 configured to generate the responsive ACK/NACK signals and CQIs as well as to generate the antenna weights that are to be applied to the transmissions from the first WTRU 12. This type of transmit diversity can achieve a performance gain from both spatial diversity and beamforming.
One issue with the transmit diversity scheme depicted in FIG. 1, however, is that it increases the required direct signaling from the data receiver, which is part of overhead to the communication link. In addition, to reduce the feedback overhead, the granularity of the feed back information for the antenna weight is usually very low.
It would therefore be beneficial to provide a method and apparatus for packet data transmission using transmit diversity weighting without explicit signaling of antenna weights.